We are using experimental animal models of early postnatal (and to some extent prenatal) malnutrition to study various biochemical, endocrinological and behavioral changes that are caused by early malnutrition with an objective of identifying those changes that become long-lasting. As these changes are identified they will be used in either devising delayed interventions or in the assessment of effectiveness of these experimental interventions. Studies that are now being started involve measurements of growth hormone, thyrotropic hormone, possibly gonadotropins, insulin, corticosterone (rats) and hydrocortisone (pigs) that will be carried out in rats and pigs. Secondly, we intend to move toward the induction of more mild degrees of malnutrition than have been used in the past. Pigs will be subjected to either calorie or protein restriction during the third to eleventh week of life followed by nutritional rehabilitation. Hormone levels in blood will be determined from birth to complete rehabilitation. Behavioral studies in pigs will involve tests of attention to secondary environmental stimuli during exposure to a primary conditioned stimulus. Other behavioral characteristics that might bear upon the nutritionally rehabilitated animal's response to new objects within the environment, including the animal's general state of emotionality, will be devised. Rats that have been malnourished postnatally will be rehabilitated and at intervals will be exposed to environmental stimulation for periods of approximately 4 weeks. Following cessation of stimulation these rats, together with appropriate control groups, will be given a battery of behavioral tests intended to measure behavioral characteristics that might be modified by latent environmental stimulation.